Programmable Logic Controllers consisting of a number of modules are used in particular in the field of automation technology. During cabling, commissioning or servicing of Programmable Logic Controllers it is normal and sensible for the modules themselves to support service activities. As a rule each module generally has a label symbolizing what type of module it is, how many channels are present/available are how these are to be connected. Mostly the channels or interfaces are directly assigned a visual status display (LED). This makes it possible to use the status display for checking even when the PLC is being cabled. The symbolic module labeling is often also affixed to the inside of a door to be opened to the side, so that a direct assignment of the label to the terminals and the status displays is possible. In some cases, with digital input modules for example, the status displays can be used even if the PLC has not yet been switched on. Direct checking of the assignment of the cabling to the digital input avoids cabling errors right from the outset.